


Don't Know Where, Don't Know When

by lilacsigil



Category: Doctor Who (2005), Harry Potter - J. K. Rowling
Genre: Community: femslash11, Crossover, F/F, Time Travel
Language: English
Status: Completed
Published: 2011-08-16
Updated: 2011-08-16
Packaged: 2017-10-22 16:34:09
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,287
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/240129
Author URL: https://archiveofourown.org/users/lilacsigil/pseuds/lilacsigil
Summary: <blockquote class="userstuff">
              <p>In 2007, Martha Jones inadvertently invents a device that affects magic. In 1944, a battle-worn Minerva McGonagall has an assignation with a secret agent. In 1995, Tonks is sent to a field with too many owls. Grindelwald's defeat depends on someone stepping outside of time.</p>
            </blockquote>





	Don't Know Where, Don't Know When

**Author's Note:**

  * For [such_heights](https://archiveofourown.org/users/such_heights/gifts).



> Thanks to st_aurafina for the epic beta!

In her medical education, Martha had learned exactly as much about physics as she needed to learn. Now that she was a science advisor to UNIT, though, she was expected to be able to make containment fields or alien detectors or death-ray deflectors at a moment's notice, and she felt distinctly lacking in that department. She was handy with the practical side of such things – design and testing – but when it came to the theory behind her work, she was lost. Her current design was a sort of temporal Geiger counter designed to detect if people or objects had travelled in time. The device was certainly detecting something, but she couldn't calibrate it any further without knowing more about temporal physics, and reading about hypothetical particles was doing her head in.

It was great to be living at the UNIT base rather than commuting from London. Everyone had their own tiny houses, which one of the Aussies had nicknamed UNIT units, and Martha could take her work home without giving the security bosses a heart attack. Right now, she was sitting on the couch, with her feet were resting on the temporal Geiger counter as she read. She glared down at the toaster-sized metal box and dropped her textbook on the couch beside her. It was late, and tachyons weren't getting any more comprehensible.

Yet another owl was perched outside on the sill, peering in. "Go away!" she yelled at the window. There were dozens of owls here, and she found their constant staring very discomforting. The other staff had laughed at her and said there weren't that many owls; that she was living in the country now and should get used to the wildlife. Martha would have thought that even a nice rolling bit of countryside with lots of rabbits and mice wouldn't have that many owls in one place, especially as they seemed to flock around her house and Lab Building #3. Martha much preferred the company of the tabby cat that had recently started showing up on her doorstep around lunchtime, licking her paws and washing her face as if she'd just had a few mice for lunch herself. The tabby was obviously someone's pet, sleek and well-kept, and Martha was happy to share the chicken or ham from her sandwich.

Martha's detection device did seem to detect items that had time-travelled but it was so ridiculously over-sensitive that it had not only detected the leather jacket that Martha had worn in the TARDIS, but the table she'd put it on and the watch she'd once worn with it. It went off when an owl flew past; it went off when someone made a cup of tea from the good urn that never went cold; it went off at one of the researchers' lucky key ring. One day it gave a red alert at the approach of one of the UNIT soldiers, Corporal Bones. Bones said that she had not, as far as she knew, ever time travelled, but she was hustled off to Psi Division for a full examination anyway. She'd never come back, so Martha hoped Psi Division hadn't done anything too awful to her.

Martha kicked the machine on, staying behind it, out of the beam of light that formed the detection field. It beeped loudly and continuously, still going berserk for no apparent reason. It was absolutely useless.

"Shut up, you bloody thing," Martha muttered, and leaned forward to switch it off, when something flickered in the detection field. Martha paused and peered closer, only to retreat in surprise when a young woman appeared right in front of her. She was staring up at the ceiling, clutching a stick, and looked equally surprised to suddenly be in Martha's tiny lounge room.

"Where did you come from?" Martha asked, not wanting to get off on the wrong foot if she'd accidentally hijacked a time traveller.

The woman straightened up, brushing her hot pink hair out of her face, and kept a firm grip on her stick. She looked confused but not frightened. "Uh, wotcha! I'm Tonks."

"Martha Jones. You're in my lounge room."

"Right then! A minute ago, I was in an open field and wondering why my boss sent me there. I suppose this is why!" Tonks didn't seem particularly troubled by her sudden change of scenery: she must have some kind of experience with such things. She had quickly assessed her location as Martha herself had been trained to do, but Tonks didn't try to run for the door or take a defensive position. She just held her ground and stared around with interest.

"Who's your boss?" Martha glared up at the window, where two owls now sat.

Tonks eyed her warily, though not with hostility. "You tell me how you made that Apparation box work, first. I didn't feel a thing!"

"Apparation?" Martha was the one lost, now.

"Oh, oh no, I did it again. You're a Muggle, aren't you?" Tonks' hair flickered from bright pink to a weird lemon colour and then a dull brown. "You used science."

"Of course I used science," Martha snapped, "What do you use, magic?"

Tonks nodded guiltily. "Sorry, yeah. You don't look too upset about it, though, Martha Jones."

Martha sat down on the couch. "Look, I'm going to refer to Clarke's Third Law here and move on."

Tonks stepped out of the detection field – Martha watched closely to see if she disappeared, but she didn't – and plopped down beside her. The beeping of the box slowed down, but didn't stop. "'Any sufficiently advanced technology is indistinguishable from magic?' That's what my dad says, but I think he's wrong."

"Well, I can't conjure up Arthur C Clarke from the dead to argue with you, but I've never found anything magical yet – amazing and far beyond my ability to understand, but not magic."

Tonks was staring at her with a stricken face and violently green hair and eyes. "Clarke's dead? Oh no, my dad will be so upset!"

"I like the way your hair changes. Yeah, Clarke died in, what, 2005?"

"I was just in 1995! Bugger! Time travel is dangerous! I don't want to end up splinching myself." She clutched Martha's arm. "Don't tell me anything else!"

Martha sat up straighter. "You don't normally travel this way?"

"No! I told you, it was your box thingy. I was standing in a field looking at all the owls and then I was here! I know what all the forms of magical transport feel like, and that wasn't one of them. I'm sure I didn't move spatially."

Martha patted her leg. "This was still a military base in 1995 – it has been since the late 60s. It's only these buildings that are new. I suppose you've just moved in time. . But don't worry, I'll get you home safely. I've had a bit of experience with time travel. Just don't go anywhere."

"I promise, I'm not!" Tonks tucked her arms and legs in to take up as little space as possible. "I've heard terrible things about wizards messing with time travel. And now I'm really cranky that my boss would send me here to get kidnapped into the future. He probably sent those owls to keep an eye out."

Martha switched off the box and flipped it on its side to unscrew the panel. "Your boss is a wizard, too? He controls owls?" She frowned. " What date was it for you, exactly?"

"Late night on the second of September, 1995."

She went over to her computer and logged in, hoping her clearance was high enough to look at the site security records. The list of incidents all the way back to 1967 was visible, if not the details. "Hey, come and look at this, Tonks."

"Um, I'd rather not. Wizards have weird effects on electronic equipment. We don't use it much."

"Oh, your technology interacts badly with ours. Okay. There's an incident report here of a humanoid figure briefly caught on camera in this area at 2218 hours, then again at 2309. You must return to 1995 in less than an hour."

"Phew, that's a relief!" Tonks relaxed and her hair turned bright pink. "I wonder why D- my boss sent me, then? If I'm going to pop right back, I mean."

"Did he give you any further instructions? To bring something with you, maybe?"

Tonks jumped to her feet and pointed her stick. "No, he only said to come to this spot. Wait, I'll show you exactly what he said. _Lerpara Lai_!"

Martha waited, but nothing happened.

Tonks looked thoroughly confused and shook the stick. " _Lerpara Lai_!". She shook it again. " _Lumos_!"

Martha touched her arm. "What are you expecting to happen?"

"The first spell should have produced my boss's voice and the second one should have made a light. It's basic stuff!"

"Spells, okay. So are there any conditions under which spells don't work?"

Tonks screwed up her face. "They're harder to do if you're emotional or really tired. Or nearly impossible if you don't have a wand to focus your magic. Oh, and you can cast a spell to limit the kinds of spells that can be cast – setting up a barrier that people can't Apparate through, for example." She saw Martha's confused look. "Teleporting. None of that should apply here! I can't do anything at all."

Tonks' hair had returned to flat brown. Holding a stray lock between her thumb and forefinger, Martha said, "But your hair colour keeps changing."

"Really? Weird! That's not a spell, though – it's an ability I have. I suppose whatever's affecting the spells isn't affecting me. No idea how that would work, though." She turned suddenly, and rather awkwardly, and her face was mere inches away from Martha's; Martha still had her fingers in Tonks' hair.

Martha could feel Tonks' breath on her face. She stayed still for a moment, then remembered Tonks' imminent deadline: less than thirty minutes from now, she'd be ten years away, untouchable. She wouldn't have another chance. She leaned forward just as Tonks did, and their noses bumped, then their lips found each other.

Somehow they ended up on the couch again, Martha's arms around Tonks, and Tonks' hands on Martha's back, under her baggy jumper, which had definitely not been meant to be seen by company. Tonks' hair rippled through rainbow colours, which made Martha laugh in delight.

"That's so pretty!"

Tonks scrubbed at her head. "I can make it behave, but my hair has always been the wildest part." Her skin changed colour to turquoise, and her features shifted to look similar to Martha's. "It's not just my hair I can change."

Martha laughed and kissed her again, to see if Tonks' bright blue lips tasted different. They didn't, but Tonks worked out what she was doing and tugged Martha's ponytail.

"I'm still me, no matter how I look!"

Worried that she'd offended, Martha was about to apologise when she saw Tonks' big grin, so she smacked her hand instead for messing up her hair. Martha's leg bumped against the device on the floor and she tried to haul her brain back on track. "Listen – if everyone where you're from can use spells, surely people know what makes them stop working."

"Not much does! Magic's sort of innate in people – not usually as much as in me, but if you're a little kid and you don't get training, magic sort of pops out all over the place. You can't switch it off." She kissed Martha again. "And you can't make magical people not be magic."

"Maybe it's a sort of field effect then – you can do what's part of you, but you can't affect anything outside yourself."

Tonks gently poked Martha in the stomach. "You're a scientist, aren't you? My dad nearly drove himself mental trying to apply science to magical theory."

"Science explains everything, eventually!"

"Yeah, it probably does – people who study arithmancy say it's all energy. But I reckon it's more like music. Everyone can hit the keys on a piano and make noise, but then you have to shape it into something, and even then everyone's going to have a different interpretation."

"Music is based on maths." Martha tucked Tonks' hair behind her ear.

"So go to a maths lecture instead of a concert. Enjoy yourself!" Tonks laughed and kissed Martha again, pulling her down onto the couch.

"Well, that's a lovely sight!"

Tonks and Martha cracked their heads together scrambling up at the sound of a new voice. Another person was suddenly in the room – a woman in a midnight blue ball gown with a big leather strap on her wrist. She was grinning widely, an expression that went rather well with her wild blonde curls and the temporal energy crackling around her.

Martha rubbed her head. "Who are you?"

"Oh, we haven't met yet? Sorry, sweetie. I'm Doctor River Song, and I'm from your future." She turned to Tonks. "And your past. Put the wand away, it won't do you any good here."

Tonks didn't put the wand away. "How did you Apparate here, then?"

River threw her head back and laughed. "Oh no, I'm a Muggle. And a time traveller, the same as Martha. I followed you here but don't worry, Dumbledore told me you'll spring back to your regular time soon."

"We know that. And what does Muggle mean?" Martha asked, suspiciously.

"Non-magical person. Most magical people wouldn't be able to access any magic at all standing near that machine of yours, Doctor Jones, but Tonks is rather special. We needed Tonks to lead me here – she's one of very few wizards whose magic we could still trace while she was near your device. " River put her foot on the box. "May I take this?"

Martha snapped "Why?" at exactly the same moment as Tonks said, "What, to wipe out magic wherever you go?"

"No, no, no. It's to help in the war." She held up a hand. "Not your war against He-Who-Must-Not-Be-Named, Tonks. He has innate abilities galore and all it would do is weaken those who fight him. It's for Dumbledore's war against Grindelwald. That's all about the wands and the spells."

"Okay," Tonks said, putting her wand in her sleeve.

"Wait, that's UNIT property and my design! It's not yours to give away!"

River smiled broadly. "Doctor Jones, may I take your machine to help in a war against evil? You have your blueprints and can easily make another one, but I'm on a tight schedule and wizards can't create this kind of technology at all."

"Well, if you put it that way. Yes, take it, go fight evil," Martha sighed. If nothing else, it might stop the creepy owl visits.

"Thank you very much! Oh, and you've only got eight minutes left!" River waved and vanished, the machine disappearing with her.

Martha glanced at the clock: 2301.

Tonks flung her arms around Martha. "I promise I'll come and look you up in 2007, but I'll be an old lady by then! I'll be nearly forty!"

"Then we'd better make today worth it." Martha grabbed a pen and wrote her phone number on Tonks' hand, then leaned in close to make the most of their minutes together. "I hear there's a war or two on."

When Tonks had vanished, Martha sat down at her computer. No wonder her machine wasn't doing what she wanted: it was vastly over-powered and calibrated far too broadly. It caused changes to energies rather than detecting them. It needed to work more delicately, like Tonks' magic, attuned to individuals and the particular changes that those people caused to the tachyon strings. The machine should detect the way people played Tonks' metaphorical piano, not play it over them. Fortunately, Martha was the perfect test subject and, she hoped, Tonks would contact her soon and be a second.

The phone didn't ring.

\---

Minerva had thought she'd feel out of place at the ball – two months ago she'd been fighting Grindelwald's forces in Budapest, and since then had been recuperating in St. Mungo's. It wasn't the first time she'd battled Grindelwald's forces, but she had never before been caught up in ones of their direct attacks. Wherever the Muggle armies had spread across Europe, Grindelwald had followed, taking advantage of the chaos to do his evil work.

Minerva's friend and schoolgirl crush Esther Greengrass had a Muggle-born mother. Esther's mother's family was in Budapest, which had been relatively safe from the deportations and murders until then. But the Nazis had entered the city, and demanded that all the Jews – including Esther's aunts and cousins – be murdered. Esther and her family could stay out of the war no longer, and neither could her friends, although most of the wizards who had tried to interfere with either the Nazis or Grindelwald had died or been imprisoned in Nurmengard.

"No." Albus had been adamant. "This is exactly the kind of situation that draws Grindelwald's attention, and we are not ready to fight him. The Order can't go."

Minerva knew that he was right. Whenever wizards crept in to help their Muggle families or friends, or besieged hometowns, Grindelwald or his assassins would be waiting to declare them blood traitors, to slaughter them and their families alike. They'd seen it in Germany, first, while Minerva had still been a schoolgirl. As the Nazis spread across Europe, Grindelwald and his army flew with them. Now the tide was turning against the Nazis but Grindelwald had no need to stop: it was the destruction and suffering that called him, not the victories. He revelled in the chaos caused by the Red Army in the east, the uprisings in Poland and the Allies pushing forward in France. Wherever wizards tried to aid Muggles, there he would be.

"He's a carrion crow," her friend Tom Riddle had said, even as he'd agreed to help Minerva and his former House Captain against Dumbledore's orders. Minerva disagreed with Tom: a carrion crow would only feed on the dead or nearly dead. Even a wolf would only pick off the weakest members of the herd and leave the rest. No, Grindelwald's evil was a very human one, preying on ties of love, family, culture, history and even plain compassion, exploiting the massive destruction of Europe to draw out the wizards who cared about anything other than the magical world.

The rescue had gone badly, as Albus had predicted. Both Esther's parents were killed; Esther herself was barely clinging to life and all her family but her grandmother and two young cousins were dead. Minerva could only recall the battle in flashes, standing back-to-back with Tom, a crying child clinging to her legs, Grindelwald's assassins swooping from the sky on black broomsticks. She'd been hit by a deflected spell and the next thing she knew she was in St. Mungo's, Esther moaning in the next bed, Tom sitting by them with a bloody bandage on his head.

Tom was somewhere in Russia now, and Minerva had been sent to a ball, of all things, to meet a contact outside from the Wizarding World, away from anywhere she was expected to be. Albus had said that it would cheer her up and she'd wanted to punch him, but in fact it was fun, being here with people who looked like her: tired and angry and shocked, but thrilled to be alive. She'd danced with two men and five women so far – women outnumbered men two to one – and, in between keeping her eyes open for her contact, had actually heard herself laughing as they spun around in a crazily fast waltz.

"Hello, darling." An older woman in a daringly cut, midnight blue dress took Minerva's hand and kissed it, her mass of blonde curls brushing against Minerva's wrist.

"Good evening," Minerva replied formally, though there was something about the woman that made her smile in excitement, as if adventure had just called her name. "Shall we dance?"

The band started playing something slower and couples were dancing close, men and women, women and women, all over the ballroom. The curly-haired woman held Minerva close, but it didn't escape Minerva's notice that she also subtly patted her down for a wand – Minerva had a secret pocket in the skirt of her emerald ballgown, as she didn't have sleeves to hide it in. Minerva looked the woman right in the eyes and did the same in return.

"I'm not a witch, sweetie, and my gun's strapped to my left thigh," she grinned.

Well, that made sense – Grindelwald would hardly suspect Muggles of carrying Albus's messages. "But you know I am, and that means you know what I can do." Minerva switched her hands on River's body so that she would be the lead, and twirled them in a slow circle across the ballroom.

"Of course I know, and I'm pretty sure you can get to that wand faster than I can get to my gun. Bloody early 20th Century underwear. My name's River, by the way. I already know your name."

"I'm sure you do," Minerva muttered, and slid her fingers over River's hips to feel for secret openings in the satin. Suddenly she found one, and her fingers stroked warm skin and thin parachute silk instead of the cool, heavy lustre of satin skirt. It would have been easy to retract her hand, but Esther's screams were still there in her mind: that could have been her, so easily. Instead she was here with a gorgeous woman and beautiful music

River turned slightly and Minerva's hand slid to her buttock instead. "Darling, we've hardly met!" Her eyes were bright, though, and Minerva grinned right back at her and danced them out the door to the courtyard garden.

There were many couples out there in the damp late-Spring night, each caught in their own world balanced between sensation and fear; everyone in their own secret nook in the little garden. Minerva shoved River against a wall and kissed her voraciously, her hand diving straight into River's underwear. River wrapped her arms around Minerva's neck – she was slightly taller than Minerva, but taller again in her enormously high heels – and threw a leg up to crook at Minerva's waist, dragging Minerva into full-body contact, eating her alive.

Minerva worked her fingers into River's body, pressing and stroking and startling her with a pinch. She was indeed wearing some kind of gun on her leg – it seemed to be made of glass, of all things, smooth and rounded – but Minerva was far more interested in the woman herself. River threw her head back and laughed before fiercely kissing her once more, their bodies pressing together exchanging heat through their glossy satin ballgowns and hidden, naked skin. The silky underwear clung to Minerva's skin like a living thing as she stroked River into shivering collapse against her.

River was hardly finished, though, spinning them around and pressing Minerva against the wall, sliding down on shaky legs to kneel at her feet. She grabbed the hem of the ballgown and threw it over her own head, kissing and nipping her way up Minerva's bare legs. Minerva had a moment to be glad she hadn't got hold of a pair of stockings, then River pulled her underwear aside and her mouth was on her and it was all Minerva could do to stay standing. She could feel River's hot fingers pushing her legs further apart, and the infuriating tickle of her hair brushing Minerva's thighs, River's breath somehow heating and cooling her wet centre at the same time. River licked a line from entrance to clit and Minerva nearly collapsed on top of her, grasping at a protruding brick to stay upright.

Minerva couldn't have said what happened in the next few minutes. She came to herself flopped down on the grass, her whole body pulsing, her exposed arms and décolletage covered in goose bumps as her sweat cooled in the night air. River lay beside her, holding her hand and softly singing along to the music of the band.

"But I know we'll meet again, one sunny day," she sang to herself, then smiled over at Minerva.

"You're going to go now, aren't you?" Minerva asked, already knowing the answer.

"Of course, and so are you." She passed Minerva a key. "What you're looking for is will be in this locker at St Pancras."

"Will be?"

River glanced at her watch. "In exactly twenty hours. It will only be there for two hours after that, so be punctual. It can't fall into the wrong hands."

Minerva sat up. "I understand. You're not scared, helping us? Grindelwald does terrible things to Muggles who associate with wizards."

River lazily poked Minerva in the side. "Good thing I'm associating with a witch, then."

Exactly twenty hours later, Minerva walked through St Pancras Station in her Muggle clothes, her heels clicking on the floor. She could see bomb damage to the rail yards outside, but the station itself was intact and she easily found the locker that matched the number on the key. Inside the locker was looking at a metal box about the size of a loaf of bread. There was a note on top.

 _Dear Minerva,_

 _Don't try to use magic on this.  
Don't Apparate.  
Hope we had a great time,_

 _Much love, River._

 _PS You're going to look great with glasses._

Minerva packed the box inside an expandable reticule that she had ready for such an occasion – it never did shrink down again afterwards – and shook her head. Glasses? That was ridiculous. Still, if it meant she'd meet River again, well, maybe it was worth it.


End file.
